The anti-Tac monoclonal antibody is known to bind to the p55 chain ofthe human interleukin 2 receptor and to inhibit proliferation of T cells by blocking interleukin 2 binding. However, use of anti-Tac as an immunosuppressant drug would be impaired by the human immune response against this murine antibody. We have therefore constructed a "humanized" antibody by combining the complementaritydetermining regions (CDRs) of the anti-Tac antibody with human framework and constant regions. The human framework regions were chosen to maximize homology with the anti-Tac antibody sequence. In addition, a computer model of murine anti-Tac was used to identify several amino acids which, while outside the CDRs, are likely to interact with the CDRs or antigen. These mouse amino acids were also retained in the humanized antibody. The humanized anti-Tac antibody has an affinity for p55 of 3 x 109 M-1, about

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into a 16-part hyperfine structure, indicating either a low concentration of V" ions and/or their existence in an unsymmetrical field. The signal for V4+ in K-ALO, consisted of a single peak, indicating a higher concentration of V" or its existence in a symmetrical field.In view of the atmospheres used in the preparations and the concentrations of V determined by analysis, it seems likely that concentration of V" is responsible for the difference between these spectra. The role of V4+ in orthorhombic S(3)-ALO, was indicated by further study of conditions favoring its formation. In air it was obtained from S(2) between 1000" and llOO°C, as described, but a sample of y-ALO, containing 10 wt% V fired at 750°C in 10%-H2-in-N1 gas and then at 800°C in Or yielded S(3)-AI20, directly.The structure of K-ALO, was studied by Brindley and Choe,' who reported the existence of two modifications obtained by heating fine-grained gibbsite. Saalfeld' observed only one type, corresponding to the form rather less frequently observed by Brindley and Choe, in the electron microscope. The present K-ALO:, gave an X-ray powder diffraction pattern which could be indexed on the larger cell given by Brindley and Choe (Table I ) and contained several lines which could not be indexed on the smaller cell found by Saalfeld, i.e. the 211, 207, 430, and 208 reflections. Samples of K-ALO~ were also prepared from a very pure fine-grained gibbsite (Na,O content 4 ppm) by the fluxing action of 5% V20, in 0, or air at 1100°C for 1 h. The relative intensities of the X-ray powder reflections were the same for this product as for that obtained from y-ALO, as described. In addition, no change in the relative intensities, e.g. of the 208 and 604 planes in particular, was observed for further samples prepared at 900" to 1080°C in the presence of V4+. No evidence was obtained, therefore, for the existence of ~-Al,0, with the smaller cell, which was present in the poorly crystalline material obtained from gibbsite. However, electron diffraction examination of these samples revealed some patterns which could be indexed on both possible a,, values, whereas others could be indexed only on the larger value. It cannot be concluded, however, that a mixture was present.Although the role of V,O, as a flux, with an effect depending on amount and temperature, is fairly straightforward, the role of the V4' ion is not. Its action is apparently required in the early stages of firing if the poorly crystalline y-Al,O,, is to be "directed" into the K-form. which could be obtained from Alumina as a Ceramic Material. Compiled and edited by W. H. Gitzen. The American Ceramic Society, Inc., Columbus, OH, 1970. 2 P. H. Rookshy; pp. 354-92 in X-Ray Identification and Crystal Structures of Clav Minerals. Edited bv G. Brown. Mineraloeical Society, London, 1961. minum Hydroxide Gels,"

The initial rates of dissolution of synthetic apatites were determined using the rotating disc method. The reactivities of carbonated apatites in acidic media were directly related to their carbonate content. This appeared to be due, in part, to a decrease in the apparent activation energy for dissolution of carbonated apatites. Structurally incorporated fluoride in carbonated apatites at levels up to 1,000 μg/g did not influence the dissolution rates, whereas fluoride at a concentration of 1 μg/ml in the buffer solution reduced the dissolution rates by 20–30%. Apatite dissolution under the experimental conditions was intermediate between transport control and surface chemical control. After 10 min, diffusion processes within the apatite pellets were found to influence the overall dissolution rate.

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